Sortation is a key added-value operation in distribution centers (DCs). Input product must be routed to its correct destination; e.g., as derived from its identification tag, such as an RFID or barcode. Sortation rate measured in cartons per minute (cpm) is a key performance measure for sorters. Other important criteria are low cost, small footprint, low noise, short (if any) downtimes, safety, reliability, fault-tolerance, and ability to handle skewed product mixes.
Two popular sortation concepts are linear sorters and circular or carousel sorters. A linear sorter is made up of one or more slat conveyors with laterally sliding shoes actuated at appropriate times to divert parcels onto fixed destination chutes. A carousel sorter is based on a circular train of bidirectional cross belts. Product is inducted by one or more induction systems; cross belts are run in one direction to accept product, and in the same or reverse direction to release it at the appropriate destination.
Linear sorters are inherently simpler in construction; however, higher rates require higher conveyance speeds and/or smaller inter-package gaps, imposing hard real-time constraints on the controller and mechanical system. Parallel utilization of linear sorters is often used when rates above the control or mechanical limits are needed. Product must be pre-sorted at the total rate to feed each linear sorter branch; the pre-sorter uptime is a crucial bottleneck for continuous operation.
Circular sorters are inherently parallel and can double as buffers; however, they require complex induct and release control (parcels must be pre-rotated, pre-gapped, etc.), and must be operated at relatively low speed to keep centrifugal forces low.
Sorters have also been proposed based on a matrix of multidirectional conveyors, a rotary accept-release unit with vertical motion, a crossbar array of shoe sorters, and others.
In a typical DC application, product is inducted into typically 30-60 induction conveyors and merged into a few (e.g., 2) “trunks,” after which it is pre-sorted and inducted (gapped) into one or more sortation units. Failure of either component implies partial (or complete) system stoppage, causing costly downtimes. Additionally, the system can only poorly compensate for product imbalance, requiring unreasonably large buffers to accommodate surges in imbalanced flow.
There is therefore presently a need for a method and system for a fault-tolerant, high-rate sortation unit that reduces or eliminates the need for both merge and induct apparatus. To the inventors' knowledge, no such techniques are currently available.